Method for sending and receiving data on a cooperative communications system and a cooperative communications method

ABSTRACT

A data transmission method of a source node in a cooperative communication system includes: performing a beamforming to a relay node; transmitting data to the relay node; performing a beamforming to a destination node; and transmitting data to the destination node.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Exemplary embodiments of the present invention relate to a method fortransmitting and receiving data in a wireless communication system; and,more particularly, to a method for transmitting and receiving data in acooperative communication system, and a cooperative communicationmethod.

2. Description of Related Art

Recently, studies have been conducted on a cooperative communicationmethod using a relay in order to improve diversity gain and throughputin a wireless communication system. In particular, many efforts havebeen made to utilize a cooperative communication method in IEEE 802.11ad using 60 GHz. The cooperative communication method using the relaymay reduce a path loss and enable a high-speed data communicationbecause a source node and a relay node cooperatively transmit data to adestination node, and may expand a service area because a signal is alsotransmitted to a destination node located far away from a source node.In such a cooperative communication method, an inter-node communicationis achieved through a wireless link of the source node—the relay node,the relay node—the destination node, and the source node—the destinationnode.

The cooperative communication method may be roughly classified into anAmplify & Forward scheme and a Decode & Forward scheme. The Amplify &Forward scheme is a scheme in which a relay node simply amplifies an RFsignal transmitted from a source node and relays the amplified RF signalto a destination node. The Decode & Forward scheme is a scheme in whicha signal received by a relay node is demodulated and decoded and thenmodulated and encoded and cooperatively transmitted to a destinationnode. Also, the cooperative communication method may be classified intoa full duplex (FD) scheme and a half duplex (HD) scheme. The full duplexscheme is a scheme in which a relay node receives a signal from a sourcenode and simultaneously relays the received signal to a destination nodeat the same time and the same frequency. The half duplex scheme is ascheme in which a relay node performs a signal transmission andreception at a different time or a different frequency.

SUMMARY OF THE INVENTION

An embodiment of the present invention is directed to a method fortransmitting and receiving data in a cooperative communication system,and a cooperative communication method, which are capable of furtherimproving diversity gain and throughput.

Other objects and advantages of the present invention can be understoodby the following description, and become apparent with reference to theembodiments of the present invention. Also, it is obvious to thoseskilled in the art to which the present invention pertains that theobjects and advantages of the present invention can be realized by themeans as claimed and combinations thereof.

In accordance with an embodiment of the present invention, a datatransmission method of a source node in a cooperative communicationsystem includes: performing a beamforming to a relay node; transmittingdata to the relay node; performing a beamforming to a destination node;and transmitting data to the destination node.

In accordance with another embodiment of the present invention, a datatransmission and reception method of a relay node in a cooperativecommunication system includes: receiving data, which is beamformed tothe relay node, from a source node; performing a beamforming to adestination node; and transmitting the received data to the destinationnode.

In accordance with another embodiment of the present invention, a datareception method of a destination node in a cooperative communicationsystem includes: receiving data, which is beamformed to the destinationnode, from a source node; and receiving the data which is beamformed tothe destination node, from a relay node, wherein the relay node receivesdata, which is beamformed to the relay node, from the source node andtransmits the received data to the destination node.

In accordance with another embodiment of the present invention, acooperative communication method includes: generating an informationsignal according to one or more of a Distributed Space Time Coding(D-STC) scheme, a Layered Modulation and Coding (LMC) scheme, and aprecoding vector switching scheme; and transmitting the informationsignal by performing a beamforming to a relay node and a destinationnode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view explaining a general cooperative communication methodusing a Distributed Space Time Coding (D-STC) scheme.

FIGS. 2 and 3 are views explaining a general cooperative communicationmethod using a Layered Modulation and Coding (LMC) scheme.

FIG. 4 is a view explaining a general cooperative communication methodusing a Network Coding (NC) scheme.

FIG. 5 is a view explaining a data transmission method of a source nodein a cooperative communication system in accordance with an embodimentof the present invention.

FIG. 6 is a view explaining a data transmission and reception method ofa relay node in a cooperative communication system in accordance with anembodiment of the present invention.

FIG. 7 is a view explaining a data reception method of a destinationnode in a cooperative communication system in accordance with anembodiment of the present invention.

FIG. 8 is a view explaining a cooperative communication method inaccordance with a first embodiment of the present invention.

FIG. 9 is a view explaining a cooperative communication method inaccordance with a second embodiment of the present invention.

FIG. 10 is a view explaining a cooperative communication method inaccordance with a third embodiment of the present invention.

FIG. 11 is a view explaining a cooperative communication method inaccordance with a fourth embodiment of the present invention.

FIG. 12 is a view explaining a cooperative communication method inaccordance with a fifth embodiment of the present invention.

FIG. 13 is a view explaining a cooperative communication method inaccordance with a sixth embodiment of the present invention.

FIG. 14 is a view explaining a cooperative communication method inaccordance with a seventh embodiment of the present invention.

FIG. 15 is a view explaining a cooperative communication method inaccordance with an eighth embodiment of the present invention.

FIG. 16 is a view explaining a cooperative communication method inaccordance with a ninth embodiment of the present invention.

FIG. 17 is a view explaining a cooperative communication method inaccordance with a tenth embodiment of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Exemplary embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings. The presentinvention may, however, be embodied in different forms and should not beconstructed as limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey the scope of the present inventionto those skilled in the art. Throughout the disclosure, like referencenumerals refer to like parts throughout the various figures andembodiments of the present invention

FIG. 1 is a view explaining a general cooperative communication methodusing a Distributed Space Time Coding (D-STC) scheme. FIG. 1 illustratesa case where all nodes use the same frequency resource and operate in anHD mode in which simultaneous transmission and reception are impossible.

As illustrated in FIG. 1, a source node 101, which is a single source,modulates data signals at a first time slot T1 for data transmission,and transmits the modulated signals A1 and A2 to a relay node 103. Therelay node 103 channel-decodes the modulated signals A1 and A2transmitted from the source node 101, and estimates (i.e., acquires)information corresponding to the modulated signals A1 and A2.

The source node 101 transmits the modulated signals A1 and A2 to thedestination node 105 at a second time slot T2. The relay node 103transmits the decoded signals—(A2)* and (A1)*, which are estimated fromthe signals A1 and A2, to the destination node 105 at the second timeslot T2. * denotes a conjugation.

The destination node 105 generates the signals A1 and A2 by decoding thesignals received from the source node 101 and the relay node 103 at thesecond time slot T2 by using a D-STC scheme.

FIGS. 2 and 3 are views explaining a general cooperative communicationmethod using a Layered Modulation and Coding (LMC) scheme. FIGS. 2 and 3illustrate a case in which all nodes use the same frequency resource andoperate in an HD mode in which simultaneous transmission and receptionare impossible.

As illustrated in FIG. 2, a source node 201 performs an LMC on data, andtransmits the LMCed signal A=αA′+βA″ to a relay node 203 and adestination node 205 at a first time slot T1. The relay node 203performs a layered demapping (Quadrature Phase Shift Keying (QPSK)demapping for each of A′ and A″) and a channel decoding on the signalreceived from the source node 201, estimates information A′ and thenestimates information A″. The destination node 205 estimates theinformation A′ through a QPSK demapping and a channel decoding on thesignal received from the source node 201.

At a second time slot T2, the source node 201 does not transmit data,and the relay node 203 transmits the information A″ among the estimatedinformation to the destination node 205. Since the destination node 205estimates the information A″ through the QPSK demapping and the channeldecoding, it may use the signal A=αA′+βA″ transmitted from the sourcenode 201.

FIG. 3 is a view explaining the LMC. A single symbol A transmitted fromthe source node 201 is modulated into A′ and A″ in a base layer and anenhancement layer, respectively. The information A′ is informationrepresenting one quadrant in the base layer, and the information A″represents a phase in the quadrant indicated by the information A′. αand β are power coefficients of A′ and A″, respectively, where α²+β²=1.

Meanwhile, in the cooperative communication methods described above withreference to FIGS. 1 and 2, one or more source nodes may transmit dataand may simultaneously transmit data in the FD scheme by using differentfrequency resources.

FIG. 4 is a view explaining a general cooperative communication methodusing a Network Coding (NC) scheme. The cooperative communication methodusing the NC scheme is used when a plurality of source nodes transmitdata. Also, the cooperative communication method using the NC scheme isan example in which a wired NC technology is applied to a wirelesscommunication.

A first source node 401 and a second source node 402 transmitinformation signals A and B including data to a relay node 403 and adestination node 405 by using a first frequency resource f1 and a secondfrequency resource f2 at a first time slot T1, respectively. The relaynode 403 and the destination node 405 estimate binary information “a”and “b” corresponding to A and B through a channel decoding at the firstfrequency resource f1 and the second frequency resource f2. The relaynode 403 performs an XOR operation on the binary information “a” and“b”, and transmits the operation information C(=a⊕b) to the destinationnode 405 at a second time slot T2.

The destination node 405 estimates the data A and B by using the binaryinformation, which is generated from the data received at the first timeslot T1, and the operation information C, which is transmitted from therelay node 403.

As described above, the cooperative communication system performs thedata transmission and reception by applying a variety of coding andmodulation schemes. In the embodiments of the present invention, data istransmitted by using a beamforming, thereby further improving diversitygain and throughput. That is, the source node and the relay nodetransmit data by performing a beamforming to a target node, and thetarget node receives data by performing a beamforming to a node whichtransmits data. Hereinafter, a method for transmitting and receivingdata in a cooperative communication system will be described in moredetail. FIGS. 5 to 7 are views explaining data transmission andreception methods of a source node, a relay node, and a destinationnode, respectively.

FIG. 5 is a view explaining a data transmission method of a source nodein a cooperative communication system in accordance with an embodimentof the present invention.

As illustrated in FIG. 5, a source node performs a beamforming to arelay node at step S501. At step S503, the source node transmits data tothe relay node. At step S505, the relay node performs a beamforming to adestination node. At step S507, the source node transmits data to thedestination node. In this case, the source node transmits the same datato the relay node and the destination node.

In order for the beamforming, the source node transmits a trainingsequence for beamforming to the relay node. The training sequence forbeamforming includes index information regarding a plurality of beamdirections. The source node receives the index information regarding thedirection selected through the training sequence from the relay node.The training sequence may have a preset length (L), and the source nodemay repetitively transmit the training sequence.

That is, the source node transmits the training sequence with respect toa plurality of beam directions covering all directions or a halfdirection (0 degree to 180 degrees, or 180 degrees to 360 degrees). Therelay node receives the training sequence and takes a correlation ineach beam direction. Then, the relay node transmits the indexinformation regarding the beam direction having the greatest correlationvalue to the source node. The relay node may previously know theinformation regarding the beam direction pattern of the trainingsequence.

The source node may perform the beamforming by forming an antennapattern using the index information so that the beam direction of theantenna is directed to the relay node. Also, the relay node may transmitdata by performing the beamforming to the destination node in theabove-described manner.

The source node and the relay node may transmit data in the HD scheme orthe FD scheme. When the source node and the relay node transmit data inthe HD scheme, the source node transmits data to the relay node at thefirst time slot and transmits data to the destination node at the secondtime slot. The relay node transmits data received from the source nodeto the destination node at the second time slot. At this time, the relaynode may also transmit data by performing the beamforming to thedestination node.

The beamforming may be performed at the first and second time slots.Alternatively, after the beamforming is performed prior to the first andsecond time slots, the data may be transmitted at the first and secondtime slots.

FIG. 6 is a view explaining a data transmission and reception method ofa relay node in a cooperative communication system in accordance with anembodiment of the present invention.

As illustrated in FIG. 6, a relay node receives data, which isbeamformed on the relay node, from a source node at step S601. At stepS603, the relay node performs a beamforming to a destination node. Atstep S605, the relay node transmits the received data to the destinationnode.

As described above with reference to FIG. 5, the relay node may performthe beamforming by transmitting a training sequence for beamforming tothe destination node. Also, the source node and the relay node maytransmit data in the HD scheme or the FD scheme. When the source nodeand the relay node transmit data in the HD scheme, the relay nodereceives data from the source node at the first time slot and transmitsdata to the destination node at the second time slot.

Meanwhile, the data received from the source node by the relay node isthe same as the data transmitted to the destination node. The relay nodemay perform a re-processing, such as a decoding and an encoding, on thereceived data.

The beamforming may be performed at the first and second time slots.Alternatively, after the beamforming is performed prior to the first andsecond time slots, the data may be transmitted at the first and secondtime slots.

FIG. 7 is a view explaining a data reception method of a destinationnode in a cooperative communication system in accordance with anembodiment of the present invention.

As illustrated in FIG. 7, a destination node receives data, which isbeamformed on the destination node, from a source node at step S701. Atstep S703, the destination node receives data, which is beamformed onthe destination node, from a relay node. The relay node receives data,which is beamformed on the relay node, from the source node andtransmits the received data to the destination node. The data relayed bythe relay node is the same as the data transmitted from the source nodeto the destination node. The relay node may perform a re-processing,such as a decoding, on the relayed data.

As described above with reference to FIGS. 5 and 6, the destination nodereceives data which is beamformed to the destination node. Thedestination node receives a training sequence and selects one of aplurality of directions. In this case, the destination node may selectone direction by taking a correlation with respect to the trainingsequence in each beam direction. The destination node transmits theindex information regarding the selected direction to the relay node andthe source node. The destination node also may receive data byperforming the beamforming to the source node and the relay node. Thatis, the destination node may perform the beamforming by forming theantenna pattern so that the beam direction of the antenna is directed tothe relay node.

Furthermore, the source node and the relay node may transmit data in theHD scheme or the FD scheme. When the source node and the relay nodetransmit data in the HD scheme, the destination node receives data atthe same time slot.

The beamforming may be performed at the first and second time slots.Alternatively, after the beamforming is performed prior to the first andsecond time slots, the data may be transmitted at the first and secondtime slots.

Meanwhile, one or more of a D-STC, an LMC, a precoding vector switching,and an NC may be additionally applied to the data transmission andreception methods described above with reference to FIGS. 5 to 7. Thatis, in accordance with the embodiment of the present invention,information signals based on one or more of the D-STC, the LMC, and theprecoding vector switching may be generated, and the information signalsmay be transmitted by performing the beamforming to the relay node andthe destination node. Alternatively, the cooperative communication maybe achieved by applying at least two schemes of the D-STC, the LMC, theprecoding vector switching, and the NC.

Hereinafter, a method for transmitting an information signal includingdata by using at least one of the D-STC, the LMC, and the precodingvector switching will be described as one embodiment. A case in which asingle source node transmits data will be described with reference toFIGS. 8 to 11. A case in which two source nodes transmit data will bedescribed with reference to FIGS. 12 to 17. Meanwhile, although QPSK or16 QAM is described as R-D link quality in FIGS. 8 to 17, the modulationscheme is not limited thereto.

FIG. 8 is a view explaining a cooperative communication method inaccordance with a first embodiment of the present invention.Specifically, FIG. 8 illustrates a cooperative communication method towhich a D-STC scheme and a precoding vector switching scheme areapplied. The cooperative communication method under an environment ofTable 1 below will be described as one embodiment.

TABLE 1    A source node and a relay node are allocated the samefrequency resource and transmit information.  The relay node can performtransmission/reception but cannot perform simultaneoustransmission/reception.  The relay node operates in an HD mode.  A QPSKmodulation scheme can be used as R-D link quality.  Each node adopts asingle antenna or multiple antennas. When the multiple antennas areadopted, the same information is transmitted through each antenna. Information (data) is transmitted using two time slots T1 and T2.

As illustrated in FIG. 8, a source node 801 transmits a QPSK-modulatedbaseband transmission signal vector A (A

{A₁, A₂}) to a relay node 803 at a first time slot T1. A₁ and A₂ may bean even symbol and an odd symbol among symbols constituting the data A.The relay node 803 estimates or generates the transmission signal vectorA by performing a QPSK demapping and a channel decoding on the signaltransmitted from the source node 801.

The source node 801 and the relay node 803 transmit the transmissionsignal vector A to a destination node 805 at a second time slot T2 byapplying a Distributed and Precoding-Vector-Switched Space Time BlockCoding (DPVS-STBC) or a DPVS Space Frequency Block Coding (DPVS-SFBC) onA. The destination node 805 estimates or acquires the transmissionsignal vector A by performing a DPVS-STBC or a DPVS-SFBC on the signalsreceived from the source node 801 and the relay node 803.

The DPVS-STBC (or DPVS-SFBC) scheme is a scheme in which a precoding isadded to the D-STC described above with reference to FIG. 1. TheDPVS-STBC (or DPVS-SFBC) scheme will be described below in more detail.

The source node 801 groups elements of the transmission signal vector Ainto two groups A₁ and A₂, and performs a QPSK modulation and precodingon each group by using two subcarriers (or two symbols). The source node801 transmits the QPSK modulated and precoded signals to the relay node803. Like the source node 801, the relay node 803 also transmits thetransmission signal vector A to the destination node 805.

The precoding is performed as expressed in Equation 1. w₁ and w₂ denoteprecoding vectors with respect to the first element and the secondelement within each group, respectively.

$\begin{matrix}\begin{matrix}{{\begin{bmatrix}w_{1}^{T} & w_{2}^{T}\end{bmatrix}\begin{bmatrix}A_{1} & {- A_{2}^{*}} \\A_{2} & A_{1}^{*}\end{bmatrix}} = {\begin{bmatrix}w_{0,1} & w_{0,2} \\w_{1,1} & w_{1,2}\end{bmatrix}\begin{bmatrix}A_{1} & {- A_{2}^{*}} \\A_{2} & A_{1}^{*}\end{bmatrix}}} \\{ {= {\underset{\underset{({{or}\mspace{14mu} {Subcarrier}\mspace{14mu} 1}}{{Symbol}\mspace{14mu} 1}}{\lbrack \begin{matrix}{{w_{0,1}A_{1}} + {w_{0,2}A_{2}}} \\{{w_{1,1}A_{1}} + {w_{1,2}A_{2}}}\end{matrix} }\underset{\underset{{{Subcarrier}\mspace{14mu} 2})}{{Symbol}\mspace{14mu} 2}}{\begin{matrix}{{{- w_{0,1}}A_{2}^{*}} + {w_{0,2}A_{1}^{*}}} \\{{{- w_{1,1}}A_{2}^{*}} + {w_{1,2}A_{1}^{*}}}\end{matrix}}}} \rbrack \begin{matrix}S \\R\end{matrix}}\end{matrix} & {{Eq}.\mspace{14mu} 1}\end{matrix}$

Using the signals transmitted by the source node 801 and the relay node803, Equation 1 will be described. The source node 801 precodes A₁ andA₂, and transmits the precoded signals w_(0,1)A₁+w_(0,2)A₂ and−w_(0,1)A*₂+w_(0,2)A*₁ to the destination node 805. The relay node 803also precodes A₁ and A₂, and transmits the precoded signalsw_(1,1)A₁+w_(1,2)A₂ and −w_(1,1)A*₂+w_(1,2)A*₁ to the destination node805. The precoding vectors w₁ and w₂ may be vectors whose independencyis maximally guaranteed, and may be used continuously used, regardlessof transmission time.

Meanwhile, in order to maximally guarantee the independent channelcharacteristic between the groups, a precoding vector switching schememay be applied. As a first embodiment using the precoding vectorswitching scheme, the precoding vectors w₁=[w_(0,1) w_(1,1)]=[1 1] andw₂=[w_(0,2) w_(1,2)]=[1 −1] may be applied to the even symbol group A₁,and the precoding vectors w₁=[1 −1] and w₂=[1 1] may be applied to theodd symbol group A₂. The opposite precoding vectors may be applied tothe even symbol group A₁ and the odd symbol group A₂.

As a second embodiment using the precoding vector switching scheme,precoding vectors w₁ and w₂ expressed as Equation 2 below may be appliedto an index K indicating the group. N is a value less than or equal tothe number of time slots for data transmission and greater than or equalto 1, and Δ is a value less than or equal to N and greater than or equalto 0.

$\begin{matrix}{{w_{1} = \begin{bmatrix}1 & ^{{\pm j}\frac{2\pi \; k\; \Delta}{N}}\end{bmatrix}},{w_{2} = {\begin{bmatrix}1 & ^{\pm {j{({\frac{2\pi \; k\; \Delta}{N} + \pi})}}}\end{bmatrix}.}}} & {{Eq}.\mspace{14mu} 2}\end{matrix}$

The generalized equation for the precoding vectors w₁ and w₂, includingthe first and second embodiments, may be expressed as Equation 3 below.X(k) and y(k) are arbitrary real numbers at which the independencybetween the two precoding vectors w₁ and w₂ is maximally guaranteed.

w ₁=[1 e ^(j2πx(k)) ], w ₂=[1 e ^(j2πy(k))].   Eq. 3

Meanwhile, as described above, a beamforming technology may be usedtogether with the D-STC scheme and the precoding vector switchingscheme. Also, in Equation 1, a case in which the precoding vectors w₁and w₂ are w₁=[1 0], w₂ =[0 1] and are modified into −A* ₂→A₂, A₂→A₁,A*₁→A₂ represents a case in which the beamforming technology is usedwithout precoding.

FIG. 9 is a view explaining a cooperative communication method inaccordance with a second embodiment of the present invention.Specifically, FIG. 9 illustrates a cooperative communication method towhich a D-STC scheme and a precoding vector switching scheme areapplied. The cooperative communication method under an environment ofTable 1 below will be described as one embodiment.

A source node 901 transmits an LMCed baseband transmission signal vectorA to a relay node 903 and a destination node 905 at a first time slotT1. The LMCed baseband transmission signal vector A may be expressed asEquation 4 below. A_(b) is a transmission signal vector of a base layer,and A_(s) is a transmission signal vector of an enhancement layer. Asdescribed above with reference to FIG. 3, α and β are power of A_(b) andA_(s), respectively.

A=αA _(b) +βA _(s).   Eq. 4

The relay node 903 estimates or generates binary information signalvectors a_(b) and a_(s) with respect to A_(b) and A_(s) by performing alayered demapping and a channel decoding on the signals transmitted atthe first time slot T1. The relay node 903 generates A_(s) from a_(s).The destination node 905 generates A_(b) by performing a layereddemapping and a channel decoding on the signals transmitted at the firsttime slot T1.

The source node 901 transmits A_(s) to the destination node 905 at asecond time slot T2, and the relay node 903 also transmits A_(s) to thedestination node 905 at the second time slot T2. The destination node905 generates A_(s) by performing a layered demapping and a channeldecoding.

At this time, the source node 901, the relay node 903, and thedestination node 905 may perform an encoding and a decoding byadditionally applying the precoding vector switching scheme describedabove with reference to FIG. 8. Also, as described above, a beamformingtechnology may be used together with the LMC scheme and the precodingvector switching scheme as described above.

FIG. 10 is a view explaining a cooperative communication method inaccordance with a third embodiment of the present invention.Specifically, FIG. 10 illustrates a cooperative communication method towhich a D-STC scheme and a precoding vector switching scheme areapplied. The cooperative communication method under an environment ofTable 2 below will be described as one embodiment.

TABLE 2    A source node and a relay node are allocated differentfrequency resources and transmit information.  The relay node canperform transmission/reception and can perform simultaneoustransmission/reception.  The relay node operates in an FD mode.  A QPSKmodulation scheme can be used as R-D link quality.  Each node adopts asingle antenna or multiple antennas. When the multiple antennas areadopted, the same information is transmitted through each antenna.

The cooperative communication method of FIG. 10 is different from thecooperative communication method of FIG. 8 in that data is transmittedusing two frequency resources. Meanwhile, the cooperative communicationmethod of FIG. 10 is identical to the cooperative communication methodof FIG. 9 in that the D-STC scheme and the precoding vector switchingmethod are applied.

As illustrated in FIG. 10, a source node 1001 transmits a QPSK-modulatedbaseband transmission signal vector A (A

{A₁, A₂}) to a relay node 1003 and a destination node 1105 at a firstfrequency resource f1. At this time, the source node 801 precodes A₁ andA₂ as expressed in Equation 1, and transmits the precoded signalsw_(0,1)A₁+w_(0,2)A₂ and −w_(0,1)A*₂+w_(0,2)A*₁. The relay node 1003estimates or generates A by performing a decoding based on a DPVS-STBCor a DPVS-SFBC.

The relay node 1003 precodes A₁ and A₂ as expressed in Equation 1, andtransmits the precoded signals w_(1,1)A₁+w_(1,2)A₂ and−w_(1,1)A*₂+w_(1,2)A*₁ to the destination node 1005 at a secondfrequency resource f2.

The destination node 1005 receives the precoded signals transmittedthrough the first and second frequency resources f1 and f2, andestimates or generates A by performing a decoding based on a DPVS-STBCor a DPVS-SFBC.

Meanwhile, as described above, a beamforming technology may be usedtogether with the D-STC scheme and the precoding vector switchingscheme. That is, the source node 1001 may perform a beamforming totransmit data to the relay node 1003 and the destination node 1005 atthe first frequency resource f1, and the relay node 1003 may transmitdata to the destination node 1005 at the second frequency resource f2.

FIG. 11 is a view explaining a cooperative communication method inaccordance with a fourth embodiment of the present invention.Specifically, FIG. 11 illustrates a cooperative communication method towhich a D-STC scheme and an LMC scheme are applied. The cooperativecommunication method under an environment of Table 3 below will bedescribed as one embodiment.

TABLE 3    A source node and a relay node are allocated the samefrequency resource and transmit information.  The relay node can performtransmission/reception and can perform simultaneoustransmission/reception.  The relay node operates in an FD mode.  A QPSKmodulation scheme can be used as R-D link quality.  Each node adopts asingle antenna or multiple antennas. When the multiple antennas areadopted, the same information is transmitted through each antenna. Information is transmitted using two time slots T1 and T2.

As illustrated in FIG. 11, a source node S transmits an LMCed basebandtransmission signal vector αA₁+βA₂ to a relay node R and a destinationnode D upon initial data transmission. The relay node R estimates orgenerates A₁ and A₂ through a layered demapping and a channel decoding.α and β are identical to those defined in FIG. 3. In subscripts of A, anodd number represents a transmission signal vector of a base layer, andan even number represents a transmission signal vector of an enhancementlayer. A_(n) represents each element constituting data which istransmitted by the source node S.

Then, the source node S transmits the LMCed baseband transmission signalvector αA₃+βA₄ to the relay node R and the destination node D at a firsttime slot T1. The relay node R generates −A*₂ by using A₁ and A₂, andtransmits −A*₂ to the destination node D. Also, the relay node Restimates A₃ and A₄ by performing a layered demapping and a channeldecoding on αA₃+βA₄.

Next, the source node S transmits A₂ to the relay node R and thedestination node D at a second time slot T2. The relay node R generatesA*₃ by using A₃ and A₄, and transmits A*₃ to the destination node D.

Again, the source node S transmits an LMCed baseband transmission signalvector αA₅+βA₆ to the relay node R and the destination node D at thefirst time slot T1. The relay node R generates −A*₄ by using A₃ and A₄,and transmits −A*₄ to the destination node D. Also, the relay node Restimates A₅ and A₆ by performing a layered demapping and a channeldecoding on αA₅+βA₆.

Again, the source node S transmits A₄ to the relay node R and thedestination node D at the second time slot T2. The relay node Rgenerates A*₅ by using A₅ and A₆, and transmits A*₅ to the destinationnode D.

Data is transmitted to the destination node D by repeating the aboveprocedures performed at the first and second time slots T1 and T2.Consequently, the destination node D receives the D-STCed signal.Therefore, the destination node D may generate necessary information byperforming a decoding and a channel decoding according to the D-STC.

Meanwhile, as described above, a beamforming technology may be usedtogether with the D-STC scheme and the LMC scheme.

FIG. 12 is a view explaining a cooperative communication method inaccordance with a fifth embodiment of the present invention.Specifically, FIG. 12 illustrates a cooperative communication method towhich an NC scheme and an LMC scheme are applied. The cooperativecommunication method under an environment of Table 4 below will bedescribed as one embodiment.

TABLE 4    First and second source nodes S1 and S2 are allocateddifferent frequency resources f1 and f2 and transmit information.  Arelay node R can perform transmission/reception but cannot performsimultaneous transmission/reception.  The relay node R transmitsinformation by using one of the frequency resources allocated to thefirst and second source nodes.  The relay node R operates in an HD mode. A QPSK modulation scheme can be used as R-D link quality.  Each nodeadopts a single antenna or multiple antennas. When the multiple antennasare adopted, the same information is transmitted through each antenna. Information (data) is transmitted using two time slots T1 and T2.

As illustrated in FIG. 12, a first source node 1201 transmits an LMCedbaseband information signal vector αA_(b)+βA_(s) to a relay node 1203and a destination node 1205 at a first time slot T1 by using a firstfrequency resource f1. A second source node 1202 transmits an LMCedbaseband information signal vector αB_(b)+βB_(s) to the relay node 1203and the destination node 1205 at the first time slot T1 by using asecond frequency resource f2.

The relay node 1203 estimates a_(s) and b_(s) by performing a layereddemapping and a channel decoding on the data signals transmitted fromthe first and second source nodes 1201 and 1202. The destination node1205 estimates a_(b), b_(b), a_(s) and b_(s) by performing a layereddemapping and a channel decoding on the data signals transmitted fromthe first and second source nodes 1201 and 1202. a_(b), b_(b), a_(s) andb_(s) represent binary information vectors of A_(b), B_(b), A_(s) andB_(s).

The relay node 1203 performs an XOR operation on a_(s) and b_(s), andtransmits the modulated signal vectors of the operation informationC(=a_(s) ⊕ b_(s)) to the destination node 1205 at the second time slotT2. The destination node 1205 estimates the operation information C byusing the signal vectors transmitted from the relay node 1203. Thedestination node 1205 finally generates a_(b), b_(b), a_(s) and b_(s) byusing the previously estimated a_(b), b_(b), a_(s) and b_(s).

Meanwhile, as described above, a beamforming technology may be usedtogether with the NC scheme and the LMC scheme. That is, the firstsource node 1201, the second source node 1202, and the relay node 1203transmit the signals based on the NC and the LMC by performing abeamforming to a target node. The beamforming technology may also beused in the methods described below with reference to FIGS. 13 to 17.

FIG. 13 is a view explaining a cooperative communication method inaccordance with a sixth embodiment of the present invention.Specifically, FIG. 13 illustrates a cooperative communication method towhich an LMC scheme is applied. The cooperative communication methodunder an environment of Table 4 will be described as one embodiment.However, instead of the QPSK modulation scheme, a 16 QAM modulationscheme is applied in the embodiment of FIG. 13.

As illustrated in FIG. 13, a first source node 1301 transmits an LMCedbaseband information signal vector αA_(b)+βA_(s) to a relay node 1303and a destination node 1305 at a first time slot T1 by using a firstfrequency resource f1. A second source node 1302 transmits an LMCedbaseband information signal vector αB_(b)+βB_(s) to the relay node 1303and the destination node 1305 at the first time slot T1 by using asecond frequency resource f2. The relay node 1303 estimates a_(s) andb_(s) by performing a layered demapping and a channel decoding on thedata signals transmitted from the first and second source nodes 1301 and1302.

The relay node 1303 generates a signal a_(s)b_(s) (or b_(s)a_(s)) byperforming a “serially concatenated binary combination” on the estimateda_(s) and b_(s). The relay node 1303 modulates the signal a_(s)b_(s) (orb_(s)a_(s)), and transmits the modulated signal vector to thedestination node 1305 at a second time slot T2.

The destination node 1305 estimates a_(s) and b_(s) from the modulatedsignal vector of the relay node 1303. The destination node 1305eliminates components corresponding to A_(s) and B_(s) from the signalreceived at the first and second time slots T1 and T2 by using theestimated a_(s) and b_(s). Therefore, the destination node 1305 mayacquire a_(b) and b_(b) through a QPSK demapping and a channel decoding.Consequently, the destination node 1305 may acquire a_(s), b_(s), a_(b)and b_(b).

Meanwhile, as described above, a beamforming technology may be usedtogether with the LMC scheme.

FIG. 14 is a view explaining a cooperative communication method inaccordance with a seventh embodiment of the present invention.Specifically, FIG. 14 illustrates a cooperative communication method towhich an NC scheme and an LMC scheme are applied. The cooperativecommunication method under an environment of Table 5 below will bedescribed as one embodiment.

TABLE 5    First and second source nodes S1 and S2 are allocateddifferent frequency resources f1and f2 and transmit information.  Arelay node R can perform transmission/reception and can performsimultaneous transmission/reception.  The relay node R transmitsinformation by using a frequency resource f3 different from thefrequency resources f1 and f2 allocated to the first and second sourcenodes.  The relay node R operates in an FD mode.  A QPSK modulationscheme can be used as R-D link quality.  Each node adopts a singleantenna or multiple antennas. When the multiple antennas are adopted,the same information is transmitted through each antenna.

As illustrated in FIG. 14, a first source node 1401 transmits an LMCedbaseband information signal vector αA_(b)+βA_(s) to a relay node 1403and a destination node 1405 by using a first frequency resource f1. Asecond source node 1402 transmits an LMCed baseband information signalvector αB_(b)+βB_(s) to the relay node 1403 and the destination node1405 by using a second frequency resource f2.

The relay node 1403 estimates a_(s) and b_(s) by performing a layereddemapping and a channel decoding on the data signals transmitted fromthe first and second source nodes 1401 and 1402. The destination node1405 estimates a_(b), b_(b), a_(s) and b_(s) by performing a layereddemapping and a channel decoding on the data signals transmitted fromthe first and second source nodes 1401 and 1402.

The relay node 1403 performs an XOR operation on a_(s) and b_(s,) andtransmits the modulated signal vectors of the operation information C(a_(s) ⊕ b_(s)) to the destination node 1405 by using a third frequencyresource f3. The destination node 1405 estimates the operationinformation C by using the signal vectors transmitted from the relaynode 1403. The destination node 1405 finally generates a_(b), b_(b),a_(s) and b_(s) by using the previously estimated a_(b), b_(b), a_(s)and b_(s).

Meanwhile, as described above, a beamforming technology may be usedtogether with the NC scheme and the LMC scheme.

FIG. 15 is a view explaining a cooperative communication method inaccordance with an eighth embodiment of the present invention.Specifically, FIG. 15 illustrates a cooperative communication method towhich an LMC scheme is applied. The cooperative communication methodunder an environment of Table 5 will be described as one embodiment.However, instead of the QPSK modulation scheme, a 16 QAM modulationscheme is applied in the embodiment of FIG. 15.

As illustrated in FIG. 15, a first source node 1501 transmits an LMCedbaseband information signal vector αA_(b)+βA_(s) to a relay node 1503and a destination node 1505 by using a first frequency resource f1. Asecond source node 1502 transmits an LMCed baseband information signalvector αB_(b)+βB_(s) to the relay node 1503 and the destination node1505 by using a second frequency resource f2. The relay node 1503estimates a_(s) and b_(s) by performing a layered demapping and achannel decoding on the data signals transmitted from the first andsecond source nodes 1501 and 1502.

The relay node 1503 generates a signal a_(s)b_(s) (or b_(s)a_(s)) byperforming a “serially concatenated binary combination” on the estimateda_(s) and b_(s). The relay node 1503 modulates the signal a_(s)b_(s) (orb_(s)a_(s)), and transmits the modulated signal vector to thedestination node 1505 by using a third frequency resource f3.

The destination node 1505 estimates a_(s) and b_(s) from the modulatedsignal vector of the relay node 1503. The destination node 1505eliminates components corresponding to A_(s) and B_(s) from the signalreceived through the first and second frequency resources f1 and f2 byusing the estimated a_(s) and b_(s). Therefore, the destination node1505 may acquire a_(b) and b_(b) through a QPSK demapping and a channeldecoding. Consequently, the destination node 1505 may acquire a_(s),b_(s), a_(b) and b_(b).

Meanwhile, as described above, a beamforming technology may be usedtogether with the LMC scheme.

FIG. 16 is a view explaining a cooperative communication method inaccordance with a ninth embodiment of the present invention.Specifically, FIG. 16 illustrates a cooperative communication method towhich an NC scheme and an LMC scheme are applied. The cooperativecommunication method under an environment of Table 6 below will bedescribed as one embodiment.

TABLE 6    First and second source nodes S1 and S2 and a relay node Rare allocated the same frequency resource and transmit information.  Therelay node R can perform transmission/reception but cannot performsimultaneous transmission/reception.  The relay node R operates in an HDmode.  A QPSK modulation scheme can be used as R-D link quality.  Eachnode adopts a single antenna or multiple antennas. When the multipleantennas are adopted, the same information is transmitted through eachantenna.  Information is transmitted using three time slots T1, T2 andT3.

As illustrated in FIG. 16, a first source node 1601 transmits an LMCedbaseband information signal vector αA_(b)+βA_(s) to a relay node 1603and a destination node 1605 at a first time slot T1. A second sourcenode 1602 transmits an LMCed baseband information signal vectorαB_(b)+βB_(s) to the relay node 1603 and the destination node 1605 atthe first time slot T2.

The relay node 1603 estimates a_(s) and b_(s) by performing a layereddemapping and a channel decoding on the data signals transmitted fromthe first and second source nodes 1601 and 1602. The destination node1605 estimates a_(b), b_(b), a_(s) and b_(s) by performing a layereddemapping and a channel decoding on the data signals transmitted fromthe first and second source nodes 1601 and 1602.

The relay node 1603 performs an XOR operation on a_(s) and b_(s), andtransmits the modulated signal vectors of the operation informationC(=a_(s) ⊕ b_(s)) to the destination node 1605 at a third time slot T3.The destination node 1605 estimates the operation information C by usingthe signal vectors transmitted from the relay node 1603. The destinationnode 1605 finally generates a_(b), b_(b), a_(s) and b_(s) by using thepreviously estimated a_(b), b_(b), a_(s) and b_(s).

Meanwhile, as described above, a beamforming technology may be usedtogether with the NC scheme and the LMC scheme.

FIG. 17 is a view explaining a cooperative communication method inaccordance with a tenth embodiment of the present invention.Specifically, FIG. 17 illustrates a cooperative communication method towhich an LMC scheme is applied. The cooperative communication methodunder an environment of Table 6 will be described as one embodiment.However, instead of the QPSK modulation scheme, a 16 QAM modulationscheme is applied in the embodiment of FIG. 17.

As illustrated in FIG. 17, a first source node 1701 transmits an LMCedbaseband information signal vector αA_(b)+βA_(s) to a relay node 1703and a destination node 1705 at a first time slot T1. A second sourcenode 1702 transmits an LMCed baseband information signal vectorαB_(b)+βB_(s) to the relay node 1703 and the destination node 1705 at asecond time slot T2. The relay node 1703 estimates a_(s) and b_(s) byperforming a layered demapping and a channel decoding on the datasignals transmitted from the first and second source nodes 1701 and1702.

The relay node 1703 generates a signal a_(s)b_(s) (or b_(s)a_(s)) byperforming a “serially concatenated binary combination” on the estimateda_(s) and b_(s). The relay node 1703 modulates the signal a_(s)b_(s) (orb_(s)a_(s)), and transmits the modulated signal vector to thedestination node 1705 at a third time slot T3.

The destination node 1705 estimates a_(s) and b_(s) from the modulatedsignal vector of the relay node 1703. The destination node 1705eliminates components corresponding to A_(s) and B_(s) from the signalreceived at the first and second time slots T1 and T2 by using theestimated a_(s) and b_(s). Therefore, the destination node 1705 mayacquire a_(b) and b_(b) through a QPSK demapping and a channel decoding.Consequently, the destination node 1705 may acquire a_(s), b_(s), a_(b)and b_(b).

Meanwhile, as described above, a beamforming technology may be usedtogether with the LMC scheme. Although a case in which one destinationnode is provided has been described with reference to FIGS. 5 to 17, thedata transmission and reception methods and the cooperativecommunication methods in accordance with the embodiments of the presentinvention can also be applied to a plurality of destination nodes.

In accordance with the exemplary embodiments of the present invention,the data is transmitted by performing the beamforming to the targetnode, thereby further improving the diversity gain and throughput of thecooperative communication system.

Furthermore, the data encoded according to one or more of the LMCscheme, the NC scheme, the D-STC scheme, and the precoding vectorswitching scheme is transmitted by performing the beamforming to thetarget node, thereby further improving the diversity gain and throughputof the cooperative communication system.

Although the embodiments of the present invention have been described inview of processes, the respective steps of the data transmission andreception methods in the cooperative communication system and thecooperative communication methods in accordance with the embodiments ofthe present invention can be easily understood in view of apparatuses.Therefore, the steps included in the data transmission and receptionmethods in the cooperative communication system and the cooperativecommunication methods in accordance with the embodiments of the presentinvention may be understood as the elements which are included in thedata transmission and reception apparatus of the cooperativecommunication system and the cooperative communication apparatusaccording to the principle of the present invention.

Specifically, the source node of the cooperative communication system inaccordance with the embodiment of the present invention includes: afirst beamforming unit configured to perform a beamforming to a relaynode; a first transmission unit configured to transmit data to the relaynode; a second beamforming unit configured to perform a beamforming to adestination node; and a second transmission unit configured to transmitdata to the destination node.

Also, the relay node of the cooperative communication system includes: areception unit configured to receive data, which is beamformed to therelay node, from a source node; a beamforming unit configured to performa beamforming to a destination node; and a transmission unit configuredto transmit the received data to the destination node.

In addition, the destination node of the cooperative communicationsystem includes: a first reception unit configured to receive data,which is beamformed to the destination node, from a source node; and asecond reception unit configured to receive the data which is beamformedto the destination node, from a relay node, wherein the relay nodereceives data, which is beamformed to the relay node, from the sourcenode and transmits the received data to the destination node.

Furthermore, the cooperative communication apparatus includes: ageneration unit configured to generate an information signal accordingto one or more of a Distributed Space Time Coding (D-STC) scheme, aLayered Modulation and Coding (LMC) scheme, and a precoding vectorswitching scheme; and a transmission unit configured to transmit theinformation signal by performing a beamforming to a relay node and adestination node.

The data transmission and reception methods and the cooperativecommunication methods in accordance with the embodiments of the presentinvention can also be embodied as computer programs. Codes and codesegments constituting the programs may be easily construed by computerprogrammers skilled in the art to which the invention pertains.Furthermore, the created programs may be stored in computer-readablerecording media or data storage media and may be read out and executedby the computers. Examples of the computer-readable recording mediainclude any computer-readable recoding media, e.g., intangible mediasuch as carrier waves, as well as tangible media such as CD or DVD.

While the present invention has been described with respect to thespecific embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

1. A data transmission method of a source node in a cooperativecommunication system, comprising: performing a beamforming to a relaynode; transmitting data to the relay node; performing a beamforming to adestination node; and transmitting data to the destination node.
 2. Thedata transmission method of claim 1, wherein said performing abeamforming to a relay node comprises: transmitting a training sequencefor beamforming to the relay node, the training sequence including indexinformation regarding a plurality of beam directions; and receivingindex information regarding a direction selected through the trainingsequence from the relay node.
 3. The data transmission method of claim1, wherein said performing a beamforming to a destination nodecomprises: transmitting a training sequence for beamforming to thedestination node, the training sequence including index informationregarding a plurality of beam directions; and receiving indexinformation regarding a direction selected through the training sequencefrom the destination node.
 4. The data transmission method of claim 1,wherein the data is transmitted to the relay node at a first time slot,and the data is transmitted to the destination node at a second timeslot.
 5. The data transmission method of claim 4, wherein the relay nodeperforms a beamforming to the destination node and transmits the data tothe destination node at the second time slot.
 6. A data transmission andreception method of a relay node in a cooperative communication system,comprising: receiving data, which is beamformed to the relay node, froma source node; performing a beamforming to a destination node; andtransmitting the received data to the destination node.
 7. The datatransmission and reception method of claim 6, wherein said performing abeamforming to a destination node comprises: transmitting a trainingsequence for beamforming to the destination node, the training sequenceincluding index information regarding a plurality of beam directions;and receiving index information regarding a direction selected throughthe training sequence from the destination node.
 8. The datatransmission and reception method of claim 6, wherein the data which isbeamformed to the relay node is received from the source node at a firsttime slot, and the received data is transmitted to the destination nodeat a second time slot.
 9. A data reception method of a destination nodein a cooperative communication system, comprising: receiving data, whichis beamformed to the destination node, from a source node; and receivingthe data which is beamformed to the destination node, from a relay node,wherein the relay node receives data, which is beamformed to the relaynode, from the source node and transmits the received data to thedestination node.
 10. The data reception method of claim 9, furthercomprising: receiving a training sequence for beamforming from the relaynode and the source node, the training sequence including indexinformation regarding a plurality of beam directions; and transmittingindex information regarding a direction selected through the trainingsequence to the relay node and the source node.
 11. The data receptionmethod of claim 9, wherein the destination node performs a beamformingto the source node and the relay node, and receives the data transmittedfrom the source node and the relay node at the same time slot.
 12. Acooperative communication method comprising: generating an informationsignal according to one or more of a Distributed Space Time Coding(D-STC) scheme, a Layered Modulation and Coding (LMC) scheme, and aprecoding vector switching scheme; and transmitting the informationsignal by performing a beamforming to a relay node and a destinationnode.
 13. The cooperative communication method of claim 12, wherein therelay node relays the information signal to a destination node byperforming a beamforming to the destination node.
 14. The cooperativecommunication method of claim 9, wherein, when a plurality of sourcenodes transmit data to the relay node and the destination node, theinformation signal is generated by additionally using a Network Coding(NC) scheme.
 15. The cooperative communication method of claim 9,wherein, in said generating an information signal, the informationsignal is transmitted at time slots respectively allocated to the relaynode and the destination node, or the information signal is transmittedusing frequencies respectively allocated to the relay node and thedestination node.